This invention relates to an improved process for drying, calcining, and sintering extruded powder materials. The process yields high strength sintered materials and substantially reduces process times and costs.
In the prior art, extruded powder shapes are generally dried or calcined by heating the extruded shapes in furnaces or kilns at low temperatures. The shapes are then sintered at higher temperatures in fossil-fueled furnaces or electric kilns. Materials such as carbides, which cannot be exposed to air and/or the products of fossil fuel combustion, are generally sintered in electric furnaces. Drying and sintering silicon carbide extruded shapes using prior art methods often requires lengthy process times of between 10-100 hours, and high energy costs and requirements.
Extruded tubes are normally sintered in the prior art in tube furnaces. The push speed of the tubes through such furnaces is normally about 3/16 inches/minute. To sinter more than one tube at a time, holes are typically bored in a solid rod material such as graphite and the tubes are loaded into these holes in the rod. The loaded rod assembly is then pushed through the tube furnace. This method results in low green/furnace load ratios and slow pushing speeds because of heat transfer limitations.